they wouldn't have gotten away with it

Valid points. And I agree with you except one. Stu wouldn't have told anyone. Remember Stu complaining because Billy was stabbing him deeper than he was supposed to. I don't think Billy intended for him to actually survive.

If it weren't for them meddling kids and that mutt!

Well, I do think they would not have gotten away with it. I think they probably had a better plan, but it seems they completely lost their mind at the end, which became their downfall. However...

"the corn syrup all over billy would have raised huge questions from the police"

Why exactly? Are they immediately going to assume that he's a serial killer who tried to trick his girlfriend into believing he was dead? If they do notice, Billy could easily explain it away as a prank at a party with drunk teens.

"FINGERPRINTS! all over the knife, the gun, the voice changer, the cellular phone. They would ahve seen that and said "why would Billy and Stu have their fingerprints on the voice changer?""

I think their behavior afterwards and any inconsistencies in their stories would raise more suspicion. If the police get a satisfying explanation from the both of them with everything pointing to their main suspect, what would the chances be of them actually bothering to compare fingerprints? The guy who did it is dead, there's no case to prove.

I think that was part of the point. They were overzealous, overconfident teenagers; they weren't criminal masterminds. They were clever to a point, but they were in way over their heads. Don't forget Gale's camcorder was hidden in the living room, too. That probably recorded audio of them laying out their plan to Sidney. Seems they would have been fucked either way.

It's small town cops most likely they wouldn't have bothered to do an investigation. Although you may be on to something about Billy keeping on killing and Stu telling somebody.

I think what would have raised flags would be the markings the duct tape would leave over Sydney's dad, on his wrists and mouth. If he was tied up like that for that for hours and hours, the tape is going to leave VERY obvious markings on those spots. I think that would be immediately questioned, why the supposed killer was tied up and gagged for a long time.

Another thing is, and this just guessing because we don't know, but if he peed his pants while tied up. If he was tied up like that for 2 days, he'll had to have peed at least once, even if they gave him no water. Again that's just pure speculation since hey, maybe they let him use the bathroom, but I think its unlikely. But add the tape marks and the soiled clothes, and I think its immediately obvious the guy was held against his will for a long time, and Billy and Stu's explanation is immediately looked into.

But regardless, I agree with another poster that they definitely would have gotten caught, and thats the point. But we don't know how, all we can do is guess. But as smart as they thought their plan was, and it was a pretty good plan in theory, something like that is NEVER 100% perfect. Maybe the evidence ends up proving it. Maybe one of them slips in their statement. Maybe one of them tells someone. The bottom line is, these were two psychotic teenagers. They'd definitely make mistakes. As we see right in the movie, they screw up a bunch at the end. Gale not being dead. Dewey not being dead. Billy stabbing Stu too deeply. Letting Sydney escape. Mistake after mistake.

The one thing they may have had going in their favor would have been small town cops. The local police force would not have been experienced enough to handle such a massive crime scene, and did a sloppy job in their investigation. It would have been possible that Billy's clothes are cut off and thrown away at the hospital. And fingerprints are never taken at the scene or on the key pieces of evidence. And if the lone survivor (Billy) is telling them what happened, and that's the way it looked, then they may have just gone with the story, and had many questions.

Remember, they were easy fooled into thinking Cotton had killed Sydney's mother, and they didn't have a clue who had killed Casey and Steve.